The use of biomass, such as plant biomass, as a raw material for the production of biofuels such as ethanol or butanol is established as a viable alternative to carbon-based fuels. Corn is the most common biomass, with a significant number of corn ethanol plants in the United States (U.S.), but other biomass sources such as sugar beets, sugar cane, milo (sorghum), barley, corn stover, energy cane, and wood waste also are used in the U.S. and other countries.
With respect to using corn as the biomass, the kernels are made up of a variety of materials including starch, protein, oils, fiber and various organic and inorganic compounds and water. The endosperm, which contains mainly starch, typically accounts for approximately 80-85% (dry weight basis) of the corn kernel whereas the germ and the hull account for approximately 10-14% and 5-6%, respectively. The germ is high in oil, typically containing approximately 38% to 45% oil by weight.
For conversion of corn (and other starch-based biomass) to biofuel, the starch is broken down (i.e. hydrolyzed) into sugars by enzymes (also known as “liquefaction”). The resultant sugars are cooled and transferred to fermentation tanks where other enzymes, are added to break down these relatively complex sugars into simple sugars (saccharification). Yeast is also added to the fermenter where these simple sugars are used by yeast to produce ethanol or another biofuel. Once fermentation has been completed, the fermented mash is transferred through the beer well to the distillation system where solids and water are separated from ethanol through a series of fractionation stages. During fractionation, ethanol is evaporated from one stage and condensed in the next stage thereby concentrating the ethanol to approximately 95 vol %. The remainder of the water is removed by molecular sieves or membranes concentrating the ethanol to greater than 99 vol %. The bulk of the water containing the soluble and insoluble solids (known as whole stillage) are discharged from the bottom of the distillation column and then centrifuged. The majority of the suspended solids are removed as a 35% solids cake while the majority of the water with dissolved solids are split into recycled liquid (backset) or sent to an evaporator for concentration. The evaporator concentrate (˜40% solids) is mixed with the cake solids and either sold in the wet state or dried in a rotary or flash dryer to a 90% solids powder know as Distillers Dry Grains with Solubles (DDGS).